[PATCH] knfsd: nfsd4: limit number of delegations handed out.

It's very easy for the server to DOS itself by just giving out too many
delegations.

For now we just solve the problem with a dumb hard limit.  Eventually we'll
want a smarter policy.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>